Positron emission tomography (PET) is emerging as an important fundamental tool for both clinical diagnosis and medical research. PET is a non- invasive medical imaging technique which provides an image of the distribution of a positron emitting radioisotope in the body. At the present time, the performance of this instrument is limited by the nuclear detectors used. The goal of the proposed project is to develop a better detector based on a new, fast, high atomic number scintillator, lead sulfate, for use in the PET instruments. Our collaborators at LBL demonstrated that lead sulfate is a very promising new scintillator material for use in PET. However, the only crystals of this material in existence were obtained from the mineral anglesite, the naturally occurring form of PbSO4. Mineral deposits of anglesite do not appear to exist with crystals of sufficient size for PET use and it is necessary to develop a method of growing these crystals in the laboratory if this promising material is to be used in future PET instruments. Our Phase I project demonstrated that it is indeed possible to grow crystals of PbSO4 in the laboratory, and that these crystals have similar scintillation properties to natural occurring crystals. Our Phase II project would perform the research necessary to produce these crystals in large sizes economically.